In a small bowl, mix egg whites, a quarter cup of milk, and lemon zest. Set aside.

In a mixing bowl, beat butter and sugar until creamy, about 2-3 minutes. Add dry ingredients and mix until combined. Slowly incorporate the egg white mixture and remaining milk.

Prepare cupcake tins with liners. Fill liners halfway and bake at 350°F for 15 minutes. Cool completely before frosting.

For frosting, beat butter until pale, then add powdered sugar, lemon zest, lemon juice, and cream. Beat until fluffy, about 3-5 minutes.

Frost cooled cupcakes with lemon buttercream using a piping bag. Serve and enjoy!